When I click the ULS on the desktop, I sometimes see "شامي" ("Shami", Levantive Arabic, apc) as one of the languages listed in the "Missing in ..." line, which is added by CX, and in the little "Translate this page" panel.

I connect from Israel. According to CLDR, and consequently, ULS/language-data, Levantine Arabic is one of the languages spoken in Israel. It's correct in real life, too, but technically, it's incorrect for CX: there is no Wikipedia in this language, so showing it in this context is useless and misleading.

apc is just an example. CX must only suggest translations into languages in which there is a Wikipedia, and which are fully supported by CX.

(I actually believe that showing not-yet-fully-supported languages in ULS is a very good idea for the future, but it's too early for it with the current infrastructure.)